eMedicine Specialties > Neurology > Electroencephalography and Evoked Potentials
EEG Seizure Monitoring
Updated: Oct 19, 2006
Introduction
EEG seizure monitoring refers to continuous 24-hour EEG monitoring for diagnosis of known or suspected seizures. A single channel often records 24-hour ECG. The recording system may monitor other physiologic measures such as oxygen saturation. EEG seizure monitoring can be performed on either an outpatient basis or an inpatient basis.
Patient Education
For excellent patient education resources, visit eMedicine's Procedures Center. Also, see eMedicine's patient education article Electroencephalography (EEG).
Outpatient EEG Seizure Monitoring
For outpatient monitoring (ambulatory EEG monitoring), the patient typically has 16 scalp electrodes. Wires connect electrodes to a small lightweight box worn on a belt or shoulder strap. The patient goes home, and the device records up to 72 hours of EEG.
The patient or family members can press an event button to mark the occurrence of a seizure. On the following day, EEG information is retrieved and reviewed. More than 1 day's EEG can be recorded with careful electrode maintenance. Home video may supplement the EEG recordings.
Inpatient EEG Seizure Monitoring
Inpatient monitoring often occurs in a specialized monitoring unit. Specially trained physicians, nurses, and technicians staff the monitoring unit. Rooms contain a vacuum supply, oxygen supply, EEG recording equipment, and one or more mounted video cameras.
Wires connect scalp electrodes to a small lightweight box. The patient wears this box on a belt or shoulder strap when ambulating. In some systems, this box transmits EEG data to one or more additional electronic components within the patient's room.
Ultimately, wireless or cable systems transmit bedside digital EEG data to a computer network. Wireless systems are less cumbersome for the patient than systems that rely on lengthy cables. Many systems will automatically store one or more hours of EEG data locally to the lightweight box when disconnection to the network occurs.
The network includes one or more workstations, database software, and a file server. Staff members view, interpret, edit, and archive data from workstations within a separate control room or at the nursing station. A more extended network may enable staff members to view data from remote hospital locations or from outside the hospital.
The monitoring unit may contain an activity room so that patients are not confined to a single hospital room all day. Continuous video and EEG recordings are documented for 24 hours or more. EEG and videos are generally reviewed every day. In some instances, portable video-EEG systems record patients in standard hospital rooms. Portable monitoring is important for the diagnosis and treatment of patients in neurology-neurosurgical intensive care units with refractory status epilepticus or unexplained encephalopathy.
The patient, visiting family, or hospital staff may press an event button to mark the occurrence of a seizure. During and after a seizure, specially trained hospital staff members examine the patient. The examination focuses on memory, orientation, attention, language, and ability to perform skilled motor movements. The staff members also make certain that no seizure-related injuries occur.
Seizures may be provoked by antiepileptic drug withdrawal, exercise, or sleep deprivation. If seizures become frequent, severe, or prolonged, the patient receives intravenous anticonvulsant treatment. Hospital personnel supervise monitoring and correct any electrode problems.
Advantages and Disadvantages of Inpatient and Outpatient EEG Seizure Monitoring
Outpatient monitoring
Advantages of outpatient monitoring include less total cost than inpatient monitoring and patients are monitored in their natural environment. Outpatient EEG seizure monitoring is useful for monitoring the frequency and duration of seizures if seizures are accompanied by a clear EEG seizure pattern in an otherwise healthy patient being treated on an outpatient basis.
Disadvantages of outpatient monitoring are that the patient does not receive continuous staff supervision, electrode problems can be corrected only once every 24 hours, video recording may be unavailable or unreliable, and the equipment is at increased risk of damage by the patient while at home.
In the future, outpatient EEG seizure monitoring devices will have a higher channel capacity. They will become more rugged and less susceptible to electrode artifacts. The wide availability of home video cameras has made outpatient video monitoring more common.
Inpatient monitoring
The advantages of inpatient monitoring are that it may provide more information than outpatient monitoring and that certain specialized procedures require inpatient monitoring. Synchronized video recordings of the patient's behavior contribute significantly to diagnosis. Video recordings of the staff's examination of the patient during or shortly after a seizure are especially useful. Rapid antiepileptic drug tapering, ictal single photon emission computed tomography (SPECT), intracranial EEG recording, and intracranial electrode brain stimulation require inpatient monitoring.
The principal disadvantage of inpatient monitoring is that it is more expensive than outpatient monitoring. In addition, some patients are less likely to have seizures outside of their natural environment. Candidates for inpatient monitoring must have events frequent enough to occur during the duration of their inpatient hospitalization.
The table below summarizes key differences between inpatient and outpatient monitoring.
Table 1. Inpatient and Outpatient Monitoring
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Table
| Feature | Outpatient | Inpatient |
| Cost | Lower | Higher |
| Natural environment recording | Yes | No |
| Video recording | Usually no | Yes |
| Number of channels | 16 (typical) | Up to 128 |
| Electrode artifacts | Common | Easily fixed |
| Presurgery evaluation | Supplementary | Supplementary |
| Medication withdrawal | No | Yes |
| Medication withdrawal | Higher | Lower |
| Intracranial EEG recording | No | Yes |
| Patient testing during event | No | Yes |
| Patients | Medically stable | All patients |
| Ictal SPECT scan | No | Yes |
| Feature | Outpatient | Inpatient |
| Cost | Lower | Higher |
| Natural environment recording | Yes | No |
| Video recording | Usually no | Yes |
| Number of channels | 16 (typical) | Up to 128 |
| Electrode artifacts | Common | Easily fixed |
| Presurgery evaluation | Supplementary | Supplementary |
| Medication withdrawal | No | Yes |
| Medication withdrawal | Higher | Lower |
| Intracranial EEG recording | No | Yes |
| Patient testing during event | No | Yes |
| Patients | Medically stable | All patients |
| Ictal SPECT scan | No | Yes |
Uses of EEG Seizure Monitoring
EEG seizure monitoring can differentiate epileptic seizures from nonepileptic disorders such as syncope, conversion disorder, parasomnias, and migraine. EEG seizure monitoring is less useful for evaluation of brief, simple partial seizures because these seizures are infrequently accompanied by significant EEG or observable behavioral changes.
Table 2. Seizure Presentation and Diagnosis
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Table
| Typical Cases | Diagnosis |
| Patient has prolonged coughing spell. He or she becomes unconscious and limp; patient has a few clonic jerks then falls to ground. EEG shows diffuse slowing. | Reflex cough syncope with clonic jerks of convulsive syncope |
| During a prolonged jerking spell, staff members are able to make patient intermittently respond verbally and follow commands. EEG shows muscle and electrode artifacts. | Conversion disorder |
| Patient arouses from sleep and appears confused and agitated. Staff can arouse patient from episode. EEG shows sleep and then an awake pattern. | Confusional arousal (parasomnia) |
| Staff interviews patient at the beginning of a typical spell. He describes a visual aura followed by a unilateral headache. EEG normal. | Migraine |
| Typical Cases | Diagnosis |
| Patient has prolonged coughing spell. He or she becomes unconscious and limp; patient has a few clonic jerks then falls to ground. EEG shows diffuse slowing. | Reflex cough syncope with clonic jerks of convulsive syncope |
| During a prolonged jerking spell, staff members are able to make patient intermittently respond verbally and follow commands. EEG shows muscle and electrode artifacts. | Conversion disorder |
| Patient arouses from sleep and appears confused and agitated. Staff can arouse patient from episode. EEG shows sleep and then an awake pattern. | Confusional arousal (parasomnia) |
| Staff interviews patient at the beginning of a typical spell. He describes a visual aura followed by a unilateral headache. EEG normal. | Migraine |
Video-EEG monitoring can determine the type of epileptic seizure. This is important because different types of seizures may require different medical therapies. Examples are differentiating absence from complex partial seizures or secondarily generalized from primary generalized convulsive seizures.
EEG seizure monitoring may detect unrecognized seizures in patients who live alone or have minimal behavioral manifestations other than confusion. For example, complex partial status epilepticus may occur as a prolonged confusional state. EEG seizure monitoring may provide information about seizure frequency and may be more reliable with outpatient monitoring when patients engage in their usual activities in their natural environment.
EEG seizure monitoring may provide information about the patient's response to antiepileptic drug therapy. In an inpatient EEG seizure monitoring unit, patients can receive intravenous loading doses. Adverse effects can be identified promptly, and drug levels obtained easily. Ineffective drugs can be discontinued quickly.
Some patients have frequent drug-resistant disabling seizures. Epilepsy surgery may benefit these patients. Sometimes, preoperative scalp EEG monitoring fails to determine the location of the epileptogenic cortex. When preoperative scalp EEG monitoring fails, the surgeon places electrodes directly on the brain surface (subdural electrodes) or in the brain (depth electrodes). Intracranial recording may occur from more than 100 recording sites. Intracranial EEG monitoring requires a sterile environment and a high EEG channel capacity.
Electrical brain stimulation may identify the location of vital brain regions such as primary motor cortex, primary sensory cortex, primary visual cortex, and language cortex. The surgeon must spare these vital brain areas during epilepsy surgery. Electrical brain stimulation is performed in the operating room during surgery or in the inpatient EEG seizure monitoring unit.
An important diagnostic test for epilepsy surgery evaluation is the ictal SPECT scan. At seizure onset, an injected radioisotope blood flow tracer delineates the seizure focus. This test can generally be performed only during inpatient EEG seizure monitoring.
Technical Considerations
Modern EEG seizure systems vary in methods of data storage, retrieval, and review. Outpatient EEG systems save EEG data on cassette tapes or solid-state memory. Inpatient EEG systems save data on hard drives.
Inpatient systems usually consist of a network that links each patient room to a central computer server. A review station displays the EEG data, which may be displayed faster than real time for rapid review. EEG recorded in a digital referential format may be displayed later in a variety of referential or bipolar montages.
Computer detection software identifies epileptiform discharges and seizures. This detection software greatly reduces the amount of EEG that needs to be reviewed. Detection is based on quantitative parameters such as wave frequency, amplitude, sharpness, rhythmicity, and duration. These parameters may be adjusted on a case-by-case basis or channel-by-channel basis to maximize sensitivity and minimize false detections. EEG and video data are archived on CD-ROM or DVD.
Sphenoidal electrodes may be used for patients with temporal lobe epilepsy. These electrodes are thin, Teflon-coated, multistrand, stainless steel wires. Pain during the first day after the procedure is common, especially when chewing. Rare complications are a transient facial palsy, infection, or wire breakage.
One method of application of these electrodes is as follows:
- The wires are sterilized.
- The distant 3-5 mm of Teflon is removed.
- The region anterior to the ears is cleaned with antiseptic.
- Lidocaine is injected along the path where the electrodes are placed.
- The distant 5-mm tip of the wire is placed in the inner lumen of the tip of a spinal needle; the remaining wire is wrapped in a spiral around the outer part of the spinal needle.
- The electrode is placed just below the inferior margin of the zygomatic arch and between the coronoid and condylar processes of the mandible, about 4 cm deep and about 2.5 cm anterior to the tragi of both ears.
- The wire is inserted by pushing the spinal needle forward.
- Once the wire is placed to the proper depth, it is removed from the spinal needle by pushing the tip of the wire out of the spinal needle with the trochanter of the spinal needle.
- The spinal needle is then removed, and the wire outside the skin surface is attached to the skin surface with collodion and gauze.
Diagnostic Utility
EEG seizure monitoring captures 50-96% of epileptic and nonepileptic events. It also establishes a diagnosis in 88-95% of cases. This technique is far superior to a single standard EEG, which demonstrates interictal epileptiform discharges in only 30% of patients with localization-related (partial) epilepsies. EEG seizure monitoring will alter management in 73% of patients. The most common changes in diagnosis are increased detection of nonepileptic episodes and generalized epileptic seizures. EEG seizure monitoring results in improved outcomes in 30-74% of patients after monitoring.
Multimedia
 | Media file 1: An EEG recording of a temporal lobe seizure. The ictal EEG pattern is shown in the rectangular areas. |
 | Media file 2: An EEG recording from a patient with primary generalized epilepsy. A burst of bilateral spike and wave discharge is shown in the rectangular area. |
 | Media file 3: An EEG recording of a seizure from a subdural array in a patient evaluated for epilepsy surgery. The subdural electrodes record from the left anterior temporal (LAT), left middle temporal (LMT), and left posterior temporal (LPT) regions. The EEG seizure pattern is seen best in bipolar EEG channels LAT 3-4and LMT 3-4 (rectangular areas). |
 | Media file 4: An MRI from a patient evaluated for spells of rhythmic leg movements. EEG seizure monitoring identified focal motor seizures arising from the contralateral cortical leg area. The MRI demonstrated a metastatic tumor at the site of the seizure focus. |
 | Media file 5: The surface of the brain of a patient undergoing epilepsy surgery evaluation. The surgeon has electrically stimulated different brain locations and labeled each location with a numbered tag. The responses to electrical stimulation may include motor movements, sensory responses and, in some cases, electrically induced partial seizures (afterdischarge). These responses are recorded and used for planning placement of a subdural electrode array and later surgery. |
 | Media file 6: A rectangular subdural electrode placed on the brain surface of a patient undergoing epilepsy surgery evaluation. |
 | Media file 7: A display of a typical video-EEG monitoring machine. Continuous multichannel EEG is displayed along with a video image of the monitored subject. |
Keywords
electroencephalogram, electroencephalograph, electroencephalography, EEG, seizure, portable video-EEG, inpatient EEG, outpatient EEG
More on EEG Seizure Monitoring |
| References |
References
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Lagerlund TD, Cascino GD, Cicora KM, Sharbrough FW. Long-term electroencephalographic monitoring for diagnosis and management of seizures. Mayo Clin Proc. Oct 1996;71(10):1000-6. [Medline].
Legatt AD, Ebersole JS. Options for long-term monitoring. In: Engel J, Pedley TA, eds. Epilepsy: A Comprehensive Textbook. Vol 1. Lippincott Williams & Wilkins; 1998: 1001-1020.
Logar C, Walzl B, Lechner H. Role of long-term EEG monitoring in diagnosis and treatment of epilepsy. Eur Neurol. 1994;34 Suppl 1:29-32. [Medline].
Pandian JD, Cascino GD, So EL, et al. Digital video-electroencephalographic monitoring in the neurological-neurosurgical intensive care unit: clinical features and outcome. Arch Neurol. Jul 2004;61(7):1090-4. [Medline].
Salinsky M, Kanter R, Dasheiff RM. Effectiveness of multiple EEGs in supporting the diagnosis of epilepsy: an operational curve. Epilepsia. Jul-Aug 1987;28(4):331-4. [Medline].
Sperling MR. Clinical challenges in invasive monitoring in epilepsy surgery. Epilepsia. 1997;38 Suppl 4:S6-12. [Medline].
Further Reading
Keywords
electroencephalogram, electroencephalograph, electroencephalography, EEG, seizure, portable video-EEG, inpatient EEG, outpatient EEG
